The present invention relates to a toroidal-type continuously variable transmission which can be used as a transmission for a car.
Now, FIG. 4 shows a conventional toroidal-type continuously variable transmission which can be used as a transmission for a car. This is a toroidal-type continuously variable transmission of a so-called double cavity type which has a structure designed for high torque. This conventional toroidal-type continuously variable, transmission is structured such that two input side disks 2, 2 and two output side disks 3, 3 are mounted on the outer periphery of an input shaft 1. Also, an output gear 4 is rotatably supported on the outer periphery of the middle portion of the input shaft 1. The two output side disks 3 and 3 are respectively connected by spline engagement to cylindrical-shaped flange portions 4a and 4a formed in the central portion of the output gear 4.
By the way, the input shaft 1 can be driven or rotated by a drive shaft 22 through a pressing device 12 of a loading cam type interposed between the input side disk 2 situated on the left side in FIG. 3 and a cam plate 7. Also, the output gear 4 is supported within a housing 14 through a partition wall 13 which is composed of two members connected together, whereby the output gear 4 can be rotated about the axis O of the input shaft 1 but is prevented from shifting in the axis O direction.
The output side disks 3 and 3 are supported in such a manner that they can be rotated about the axis O of the input shaft 1 by their respective needle roller bearings 5 and 5 interposed between the input shaft 1 and output side disks 3, 3. On the other hand, the input side disks 2 and 2 are supported on the two end portions of the input shaft 1 through their respective ball splines 6 and 6 in such a manner that they can be rotated together with the input shaft 1. Also, as shown in FIG. 7 as well, power rollers 11 are rotatably held by and between the inner surfaces (concave surfaces) 2a, 2a of the respective input side disks 2, 2 and the inner surfaces (concave surfaces) 3a, 3a of the respective output side disks 3, 3.
Between the input side disk 2 situated on the left side in FIG. 4 and cam plate 7, there is interposed a first countersunk plate spring 8; and, between the input side disk 2 situated on the right side in FIG. 4 and loading nut 9, there is interposed a second countersunk plate spring 10. These countersunk plate springs 8 and 10 apply pressing forces to the mutual contact portions between the concave surfaces 2a, 2a, 3a, 3a of the respective disks 2, 2, 3, 3 and the peripheral surfaces 11a, 11a (see FIG. 7) of the power rollers 11, 11.
Therefore, in the continuously variable transmission having the above structure, in case where a rotational force is input into the input shaft 1 from the drive shaft 22, the two input side disks 2 and 2 are rotated integrally with the input shaft 1, and the rotational movements of the input side disks 2 and 2 are transmitted by the power rollers 11 and 11 to the output side disks 3 and 3 at a given transmission ratio. Also, the rotational movements of the output side disks 3 and 3 are transmitted from the output gear 4 to an output shaft 17 through a transmission gear 15 and a transmission shaft 16.
By the way, in the thus structured continuously variable transmission, generally, in order to prevent the needle roller bearing 5, which supports the output disk 3 rotatably, from shifting in the axis O direction of the input shaft 1 and thus slipping out of its given position, there is disposed slippage preventive means for preventing the slippage of the needle roller bearing 5.
Here, FIG. 5 shows a conventional example of such needle roller bearing 5 slippage preventive means (see JP-A-11-166605). As shown in FIG. 5, the slippage preventive means is composed of a retaining ring (slippage preventive member) 18; and, specifically, the retaining ring 18 has a substantially rectangular section shape and is fitted into and secured to a ring-shaped securing groove 3b formed in the inner peripheral surface of the output side disk 3 (that is, the peripheral surface of a stepped-penetration hole 30 formed in the output side disk 3). That is, the retaining ring 18 prevents the needle roller bearing 5 from shifting in the axis O direction (that is, from slipping off the output side disk 3).
Also, as shown in FIG. 6, the ball spline 6 supporting the input side disk 2 includes a first ball spline groove 31 (see FIG. 4) formed in the outer peripheral surface of the input shaft 1, a second ball spline groove 32 formed in the inner peripheral surface of the input side disk 2 (the peripheral surface of a penetration hole 43 formed in the input side disk 2), and a plurality of balls 33 rollably interposed between the first and second ball spline grooves 31 and 32. And, in order to prevent the balls 33 from slipping in the axial direction of the input shaft 1, there is disposed slippage preventive means which is used to prevent the balls 33 against slippage.
Such slippage preventive means, for example, as shown in FIG. 6, is composed of a retaining ring (slippage preventive member) 35 having a circular-shaped section which is fitted into and secured to a ring-shaped securing groove 2b formed in the inner peripheral surface of the input side disk 2; that is, the retaining ring 35 prevents the balls from shifting in the axis O direction of the input shaft 1 (namely, from slipping out of the input side disk 2).
By the way, as can be seen from FIG. 5, the conventional retaining ring 18 is structured such that its section has a substantially rectangular shape and, therefore, the securing groove 3b, to which the retaining ring 18 is to be secured, is also structured such that its section has a substantially rectangular shape. That is, when observing the securing groove 3b through its section shown in FIG. 5 (b), the securing groove 3b includes a bottom surface (groove bottom) p and two side surfaces q, q which extend from the bottom surface p toward the penetration hole 30 of the output side disk 3; and, the bottom surface p is formed linear (straight) and, at the same time, the bottom surface p and two side surfaces q, q are connected to each other through their respective arc-shaped surfaces the sections of which respectively have a small radius of curvature.
Also, as can be understood from FIG. 6, in the case of the conventional retaining ring 35, its section has a circular shape and, therefore, the securing groove 2b for securing the retaining ring 35 thereto is also structured such that its section has a circular shape. That is, when observing the securing groove 2b through its section shown in FIG. 6(b), the bottom surface r and two side surfaces s, s of the securing groove 2b are continuously connected together as a surface the section of which has an arc-like shape.
However, as shown in FIG. 5(b), in case where the two corners R1, R1 of the groove bottom of the securing groove 3b, that is, the two connecting portions R1, R1 between the bottom surface p and two side surfaces q, q are respectively formed as a surface the section of which has an arc shape with a small radius of curvature, when, as shown in FIG. 7, in order to increase a transmission ratio, the power roller 11 is shifted and a force in the arrow mark F direction is thereby applied to the securing groove 3b, stresses are concentrated on the groove bottom of the securing groove 3b, especially, on the corner portions (connecting portions) R1, R1. Therefore, there is a fear that, when transmitting high torque, the yield strength of the output side disk 3 can be short.
On the other hand, as shown in FIG. 6(b), in case where the bottom surface r and two side surfaces s, s of the securing groove 2b are formed as a continuous arc-shaped surface and thus the two connecting portions R2, R2 are each formed as an arc-shaped surface having a large radius of curvature, even when a force from the power roller 11 is applied to the securing groove 2b, stresses acting on the two corner portions R2, R2 of the securing groove 2b can be dispersed and released, thereby being able to enhance the yield strength of the input side disk 2. However, when the ball 33 collides with the retaining ring 35, since the area of the side surface q of the securing groove 2b, which intersects at right angles to the moving direction (axis O direction) of the ball 33 and is used to receive the retaining ring 35, is small, the retaining ring 35 is easy to slip out of the securing groove 2b. 
The present invention aims at eliminating the drawbacks found in the above-mentioned conventional toroidal-type continuously variable transmission. Accordingly, it is an object of the invention to provide a toroidal-type continuously variable transmission which not only can ease concentration of stresses on the securing groove to which the slippage preventive member for a needle roller bearing or for the ball of a ball spline is to be secured, but also can make it difficult for the slippage preventive member to slip out of the securing groove.
In attaining the above object, according to a first aspect of the invention, there is provided a toroidal-type continuously variable transmission, comprising:
an input shaft to which a rotational force is input;
a first disk disposed concentric with the input shaft and including a penetration hole formed in a central portion thereof, the first disk acting as one of input side disk and output side disk, the input shaft passing through the penetration hole;
a needle roller bearing interposed between the input shaft and the first disk for rotatably supporting the first disk;
a slippage preventive member secured to an inner peripheral surface of the penetration hole formed in the first disk, for preventing the needle roller bearing from slipping out in an axial direction of the input shaft; and,
a securing groove formed in the inner peripheral surface of the penetration hole formed in the first disk, for securing the slippage preventive member thereto.
In the first aspect of the present invention, the securing groove includes first and second side surfaces opposed to each other and a bottom surface interposed between the first and second side surfaces so as to define a substantially U-shape in a cross section of the securing groove. Further, the securing groove further includes, a first connecting portion with a cross section thereof having an arc-like shape for connecting the bottom surface with one of the side surfaces that is situated on the needle roller bearing side, and a second connecting portion with a cross section thereof having an arc-like shape for connecting the bottom surface with the other of side surfaces. Moreover, the radius of curvature of the first connecting portion is larger than the radius of curvature of the second connecting portion.
In addition, the above-mentioned object can also be achieved by a toroidal-type continuously variable transmission, according to the second aspect of the present invention comprising:
an input shaft to which a rotational force is input;
an input side disk rotatable integrally with the input shaft;
an output side disk disposed concentric with and opposed to the input side disk;
a ball spline for supporting the input side disk on an outer peripheral surface of the input shaft, the ball spline including a first ball spline groove formed in the outer peripheral surface of the input shaft, a second ball spline groove formed in an inner peripheral surface of the input side disk, and a plurality of balls rollably interposed between the first and second ball spline grooves;
a slippage preventive member for preventing the balls from slipping out in an axial direction of the input shaft;
a securing groove formed in the input shaft or in the input side disk, for securing the slippage preventive member thereto.
In the second aspect of the present invention, the securing groove includes first and second side surfaces opposed to each other and a bottom surface therebetween so as to define a substantially U-shape in a cross section of the securing groove. The securing groove includes a first connecting portion with a cross section thereof having an arc-like shape for connecting the bottom surface with one of the side surfaces that is situated on the ball spline groove side, and a second connecting portion with the section thereof having an arc-like shape for connecting the bottom surface with the other of the side surfaces. The radius of curvature of the first connecting portion is larger than the radius of curvature of the second connecting portion.
According to the first and second aspects of the present invention, stresses acting on the securing groove are dispersed and released along the arc-shaped surface having a large radius of curvature of the first connecting portion of the securing groove. Therefore, concentration of the stresses on the first connecting portion of the securing groove can be eased, thereby being able to enhance the yield strength of the output side disk, input side disk or input shaft.
On the other hand, in the case of the second connecting portion of the securing groove that is situated on the opposite side to the needle roller bearing or to the ball of the ball spline, since it is formed as an arc-shaped surface having a small radius of curvature, the area of the side surface thereof, which intersects at right angles to the moving direction of the needle roller bearing or the ball of the ball spline and is used to receive the slippage preventive member when the needle roller bearing or the ball is collided with the slippage preventive member, is wide. As a result of this, the slippage preventive member can be made difficult to slip out of the securing groove.
Also, according to a toroidal-type continuously variable transmission of the invention, the section shape of the portion of the slippage preventive member to be inserted into the securing groove is formed substantially coincident with the section shape of the securing groove, and the slippage preventive member is fitted with and secured to the securing groove in such a manner that the outer peripheral surface of the insertion portion of the slippage preventive member is substantially coincident with the inner peripheral surface of the securing groove. This makes it more difficult for the slippage preventive member to slip out of the securing groove.